Ink compositions for ink jet printing

ABSTRACT

Radiation curable ink compositions for ink jet contain radiation curable monomers containing vinylether and acrylate functions.

This application is a REI of Ser. No. 09/396,867 filed Sep. 15, 1999,now U.S. Pat. No. 6,310,115, which claims the benefit of U.S.Provisional Application No. 60/113,339 filed Dec. 22, 1998, which isexpired.

FIELD OF THE INVENTION

The present invention relates to ink compositions for ink jet printingcontaining a particular type of radiation curable compounds.

BACKGROUND OF THE INVENTION

In the majority of applications printing proceeds by pressure contact ofan ink-loaden printing form with an ink-receiving material which isusually plain paper. The most frequently used impact printing techniqueis known as lithographic printing based on the selective acceptance ofoleophilic ink on a suitable receptor.

In recent times however so-called non-impact printing systems havereplaced classical pressure-contact printing to some extent for specificapplications. A survey is given e.g. in the book “Principles of NonImpact Printing” by Jerome L. Johnson (1986), Palatino Press, Irvine,Calif. 92715, USA.

Among non-impact printing techniques ink jet printing has become apopular technique because of its simplicity, convenience and low cost.Especially in those instances where a limited edition of the printedmatter is needed ink jet printing has become a technology of choice. Arecent survey on progress and trends in ink jet printing technology isgiven by Hue P. Le in Journal of Imaging Science and Technology Vol. 42(1), January/February 1998, which is hereby included as reference.

In ink jet printing tiny drops of ink fluid are projected directly ontoan ink receptor surface without physical contact between the printingdevice and the receptor. The printing device stores the printing dataelectronically and controls a mechanism for ejecting the dropsimage-wise. Printing is accomplished by moving the print head across thepaper or vice versa. Early patents on ink jet printers include U.S. Pat.No. 3,739,393, U.S. Pat. No. 3,805,273 and U.S. Pat. No. 3,891,121.

The jetting of the ink droplets can be performed in several differentways. In a first type of process a continuous droplet stream is createdby applying a pressure wave pattern. This process is known as continuousink jet printing. In a first embodiment the droplet stream is dividedinto droplets that are electrostatically charged, deflected andrecollected, and into droplets that remain uncharged, continue their wayundeflected, and form the image. Alternatively, the charged deflectedstream forms the image and the uncharged undeflected jet is recollected.In this variant of continuous ink jet printing several jets aredeflected to a different degree and thus record the image(multideflection system).

According to a second process the ink droplets can be created “ondemand” (“DOD” or “drop on demand” method) whereby the printing deviceejects the droplets only when they are used in imaging on a receiverthereby avoiding the complexity of drop charging, deflection hardware,and ink recollection. In drop-on-demand the ink droplet can be formed bymeans of a pressure wave created by a mechanical motion of apiezoelectric transducer (so-called “piezo method”), or by means ofdiscrete thermal pushes (so-called “bubble jet” method, or “thermal jet”method).

Ink compositions for ink jet typically include following ingredients:dyes or pigments, water and/or organic solvents, humectants such asglycols, detergents, thickeners, polymeric binders, preservatives, etc.It will be readily understood that the optimal composition of such anink is dependent on the ink jetting method used and on the nature of thesubstrate to be printed. The ink compositions can be roughly divided in:

-   water based: the drying mechanism involves absorption, penetration    and evaporation;-   oil based: the drying involves absorption and penetration;-   solvent based: the drying mechanism involves primarely evaporation;-   hot melt or phase change: the ink vehicle is liquid at the ejection    temperature but solid at room temperature; drying is replaced by    solidification;-   UV-curable: drying is replaced by polymerization.

It will be readily understood that the first two types of inkcompositions require a receiving medium that is more or less absorptive.On the contrary, for non-absorbent substrates solvent based inks, hotmelt inks or UV-curable inks will be better suited.

Early patents on water-based inks include U.S. Pat. No. 3,903,034, U.S.Pat. No. 3,889,269, U.S. Pat. No. 3,870,528, U.S. Pat. No. 3,846,141,U.S. Pat. No. 3,776,742 and U.S. Pat. No. 3,705,043. however, it wasrecognized early that systems based on water-based inks suffer from anumber of disadvantages such as: (a) they require water evaporation andtherefore an extensive drying system, especially when printing speed isimportant; (b) large printed areas tend to cockle, (c) the images aresensitive to wet and dry rubbing, (d) inks of low viscosity tend to tipdry on the orifice which can be avoided by the use of humectants, usallyglycols, which then increase viscosity. The use of polar solvent basedinks can overcome some of the problems inherent to water-based inks, butin its turn causes other problems such as the possible generation oftoxic or inflammable vapours. Therefore efforts were conducted to thedevelopment of low-solvent ink compositions. In this research theconcept of UV-curable ink compositions was generated, of which a surveyis given hereinafter.

An important basic patent on ink compositions for ink jet, satisfyingthe need for a low solvent content, and containing a UV-curable compoundis U.S. Pat. No. 4,303,924. It describes an ink jet printing processusing charged droplets wherein the ink composition contains (a) amultifunctional unsaturated UV-curable compound, (b) a monofunctionalunsaturated compound, (c) a reactive synergist, (d) a colorant, (e) anoil soluble salt for conductivity, (f) a photoinitiator, and (g) anorganic polar solvent, preferably in a small amount. Several examples ofmonomers containing acrylate, epoxy, and vinyl functional groups aredisclosed.

In EP 0 071 345 a jet ink composition is claimed comprising (a) acationically polymerizable epoxy resin chosen from particular classes,(b) a photoinitiator, (c) a colorant, (d) a blend of organic solvents.

In U.S. Pat. No. 4,680,368 a UV-curable ink, not limited to ink jet, isdisclosed comprising (A) a poly(urethane(meth)acrylate), (B) a radicallypolymerizable compound and (C) a photoinitiator.

According to U.S. Pat. No. 4,978,969 the ink composition comprises12-80% of a UV curable adhesive, 3-10% of a pigment, and 10-40% of asolvent.

In EP 0 456 039 B1 an ink composition for ink jet is disclosed that isfree of volatile organic solvent and contains a colorant, a polarconductive compound, and one or more monomers. In the analogous EP 0 540203 B1 a non-conductive ink composition, free of volatile solvent, isdisclosed, said composition again comprising one or more monomers and acolorant.

In U.S. Pat. No. 5,270,368 the ink composition contains at least twoacrylate types, being an aromatic acrylate with carboxyl groups, and anepoxy acrylate.

According to EP 0 658 607 an aqueous ink contains a pigment, awater-soluble resin for dispersing the pigment, a water-solubleUv-curable monomer and a photoinitiator.

In U.S. Pat. No. 5,623,001 an ink is described comprising (a) 20-75%water, (b) a water-mixable UV-curable compound, preferably an acrylateoligomer, (c) a photoinitiator and (d) a colorant.

According to U.S. Pat. No. 5,641,346 the ink jet ink contains acolorant, a liquid phase comprising water, and an epoxy compound and/ora vinyl ether compound.

In WO 97/31071 a radiation-curable ink jet composition is describedcomprising from 80% to 95% of a polyfunctional (poly)alkoxylatedacrylate monomer.

Summarizing, a radiation curable ink compositions may in general containone or more radiation curable prepolymers, or oligomers, radiationcurable monomers or reactive diluents, optionally one or morephotoinitiators, colorants, and other additives. Although polymerizablemonomers are in principle suited for achieving low viscosity, needed inink jet printing, without introducing a significant amount of water orother solvent, it is a problem to find monomers that are suited for useboth in free radically and cationically radiation curable inks.

The present invention extends the teachings on radiation curable inkcompositions for ink jet.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide new radiationcurable compounds for radiation curable inks.

It is another object of the present invention to provide new reactivediluents for radiation curable inks.

It is a further object of the present invention to provide inkcompositions for ink jet printing containing these new compounds.

These and other objects of the invention will become apparent from thedescription hereinafter.

SUMMARY OF THE INVENTION

The above mentioned objects are realized by providing an ink compositioncontaining a radiation-curable monomer represented by the followinggeneral formula I:

-   -   wherein,    -   R¹ represents hydrogen, or a substituted or unsubstituted alkyl        group, preferably methyl,    -   L represents a linking group,    -   X represents O, S or NR² wherein R² has the same meaning as R¹;        when X=NR², L and R² may form together a ring system,    -   n and m independently represent a value from 1 to 5.

DETAILED DESCRIPTION OF THE INVENTION

Representative examples of compounds corresponding to general formula Iare listed in the following table 1 without being limited thereto.

TABLE 1 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.10

1.11

1.12

1.13

1.14

1.15

1.16

1.17

1.18

1.19

1.20

1.21

1.22

1.23

1.24

1.25

1.26

The compounds of table 1 can be prepared according to standard syntheticmethods known to those skilled in the art of organic synthesis. Apossible pathway is depicted in the following scheme 1.

An actual preparative example is given furtheron.

We will now describe systematically the principal other ingredients ofthe ink composition according to the invention.

Initiators

In a preferred embodiment, the initiator is a photoinitiator. Thephotoinitiators can be divided in compounds that are suited for cationicpolymerization and compounds suited for free radical polymerization.

References on photoinitiators include following: P. K. T. Oldring (ed.),“Chemistry and Technology of UV and EB Formulation for Coatings, Inksand Paints: Vol. 3 Photoinitiators for Free Radical and CationicPolymerization,” SITA Technology Ltd., London, UK (1991); N. S. Allen,“Photoinitiators for UV and visible curing of coatings; mechanism andproperties”, Journal of Photochemistry and Photobiology, A: Chemistry100 (1996) 101-107; J. V. Koleske, “A radiation-cure primer”, Journal ofCoatings Technology, Vol69, No. 866, March 1997, 29-38.

Disclosures specific on photoinitiators for cationic polymerisationinclude: J. V. Crivello, “The Chemistry of Photoacid GeneratingCompounds”, Proceedings of the ACS Division of Polymeric Materials:Science and Engineering, Vol. 61, pages 62-66, (1989); J. V. Crivelloand J. H. W. Lam, “Complex Triarylsulfonium Salt Photoinitiators I. TheIdentification, Characterization, and Synthesis of a New Class ofTriarylsulfonium Salt Photoinitiators,” Journal of Polymer Science,Polymer Chemistry Edition, Vol. 18, 2677-2695 (1980); J. V. Crivello andJ. H. W. Lam, “Complex Triarylsulfonium Photoinitiators II. ThePreparation of Several New Complex Triarylsulfonium salts and theInfluence of Their Structure in Photoinitiated Cationic Polymerization,”Journal of Polymer Science, Polymer Chemistry Edition, Vol. 18, pages2697-2714 (1980); J. V. Crivello and J. H. W. Lam, “Diaryliodonium SaltsA New Class of Photoinitiators for Cationic Polymerization,”Macromolecules, Vol. 10, pages 1307-1315 (1977); and J. V. Crivello, J.L. Lee and D. A. Conlon, “Developments in the Design and Applications ofNovel Thermal and Photochemical Initiators for Cationic Polymerization”,Makromol. Chem. Macromolecular Symposium, Vol. 13/14, pages 134-160(1988).

Particularly preferred are the diaryl iodonium salts and theirderivatives, the triaryl sulfonium salts and their derivatives, and thetriphenyl phosphonium salts and their derivatives, with examples ofalkyl and aryl substituents. Very recently, there have been describednew types of photoinitiators for cationic polymerization such astriarylsulphonium-tetrakis(pentafluorophenyl)-borate (RHODORSIL 2074,Rhône-Poulenc Chimie), by C. Priou et al. in the Conference Proceedingsof Radtech Europe '97, p. 314, and such as onium salts with specificlight absorption characteristics in WO 97/47660 (Nippon Kayaky KK).

Useful photoinitiators for free radical polymerization are e.g. LUCIRINLR8953 (ex BASF), IRGACURE 819 and 907 (ex Ciba-Geigy), DAROCUR 4865 (exCiba-Geigy), and isopropylthioxanthones, e.g. QUANTACURE ITX (ex RahnAG). Other useful photoinitiators for free radical polymerization arepolymeric oligomeric, respectively copolymerizable photoinitiators suchas discussed by M. Visconti et al. respectively W. Davies et al. in theConference papers 6, respectively 7, of the Radcure Coatings and Inks,Curing and Performance Conference (Harrogate, 22-23 June 1998). Suchphotoinitiators are e.g. ESACURE KIP150, ESACURE KT 37 and KT 55 (exLamberti), and acrylated IRGACURE 2959 or IRGACURE 2959 modifiedmelamine acrylate (ex Ackros Chemicals).

Additional examples of suitable initiators are disclosed in followingpatents: U.S. Pat. Nos. 4,683,317, 4,378,277, 4,279,717, 4,480,368,4,443,495, 4,303,924, 4,751,102, 4,334,970, 5,270,368, 5,395,724, and EP0 540 203, EP 0 568 607 and EP 0 659 039.

All disclosures cited are totally incorporated herein by reference.

Sometimes, it is also desirable to include, as well as a primaryphotoinitiator, a co-initiator, also called initiator synergist which ispreferably of the amine type, e.g. the aminobenzoate type. The lattertypes of co-initiators are generally being used with the benzophenone orxanthone/thioxanthone types of primary photoinitiator. More examples canbe found in the Oldring reference cited above.

The photoinitiator and occasionally the coinitiator are preferablypresent in an amount from 0.2 to 20 % by weight and most preferablybetween 1 and 10 %.

Colorants

Inks of the present invention preferably contain a colorant. Anycolorant may be used to impart the desired color to the ink. Inembodiments of the present invention the colorant may include at leastone pigment, one dye, or a combination thereof.

A wide variety of organic and inorganic dyes and pigments, alone or incombination may be selected for use in the ink compositions of thisinvention. The pigment particles should be sufficiently small to permitfree flow of the ink through the ink jet printing device, especially atthe ejecting nozzles that usually have a diameter ranging from 10 μm to50 μm. The pigment particle size also has an influence on the pigmentdispersion stability, which is critical throughout the life of the ink.It is also desirable to use small particles for maximum color strength.

Accordingly, the average particle diameter may be from about 0.005 μm toabout 15 μm. Preferably, the pigment particle size may range from about0.005 to about 5 microns, more preferably from about 0.005 to about 1μm, and most preferably from about 0.005 to about 0.3 μm. Pigmentparticle sizes outside these ranges may, of course, be used as long asthe objectives of the present invention are achieved.

Very fine dispersions of pigments and methods for their preparation aredisclosed in e.g. EP 0 776 952, U.S. Pat. No. 5,538,548, U.S. Pat. No.5,443,628, EP 0 259 130, U.S. Pat. No. 5,285,064, EP 0 429 828, and EP 0526 198.

The pigment can be black, cyan, magenta, yellow, red, blue, green,brown, mixtures thereof, and the like. For example, suitable pigmentmaterials include carbon blacks such as Regal 400R, Mogul L, Elftex 320from Cabot Colo., or Carbon Black FW18, Special Black 250, Special Black350, Special Black 550, Printex 25, Printex 35, Printex 55, Printex 150Tfrom Degussa Co., and Pigment Black 7. Additional examples of suitablepigments are disclosed in, for example, U.S. Pat. No. 5,389,133, toGundlach et al., the entire disclosure of which is incorporated hereinby reference.

Suitable pigments include, for instance, C. I. Pigment Yellow 17, C. I.Pigment Blue 27, C. I. Pigment Red 49:2, C. I. Pigment Red 81:1, C. I.Pigment Red 81:3, C. I. Pigment Red 81:x, C. I. Pigment Yellow 83, C. I.Pigment Red 57:1, C. I. Pigment Red 49:1, C. I. Pigment Violet 23, C. I.Pigment Green 7, C. I. Pigment Blue 61, C. I. Pigment Red 48:1, C. I.Pigment Red 52:1, C. I. Pigment Violet 1, C. I. Pigment White 6, C. I.Pigment Blue 15, C. I. Pigment Yellow 12, C. I. Pigment Blue 56, C. I.Pigment Orange 5, C. I. Pigment Black 7, C. I. Pigment Yellow 14, C. I.Pigment Red 48:2, C. I. Pigment Blue 15:3, C. I. Pigment Yellow 1, C. I.Pigment Yellow 3, C. I. Pigment Yellow 13, C. I. Pigment Orange 16, C.I. Pigment Yellow 55, C. I. Pigment Red 41, C. I. Pigment Orange 34, C.I. Pigment Blue 62, C. I. Pigment Red 22, C. I. Pigment Red 170, C. I.Pigment Red 88, C. I. Pigment Yellow 151, C. I. Pigment Red 184, C. I.Pigment Blue 1:2, C. I. Pigment Red 3, C. I. Pigment Blue 15:1, C.I.Pigment Blue 15:3, C.I. Pigment Blue 15:4, C. I. Pigment Red 23, C. I.Pigment Red 112, C. I. Pigment Yellow 126, C. I. Pigment Red 169, C. I.Pigment Orange 13, C. I. Pigment Red 1-10, 12, C.I. Pigment Blue 1:X,C.I. Pigment Yellow 42, C.I. Pigment Red 101, C.I. Pigment Brown 6, C.I. Pigment Brown 7, C. I. Pigment Brown 7:X, C. I. Pigment Black 11, C.I. Pigment Metal 1, C. I. Pigment Metal 2, C.I. Pigment Yellow 128, C.I.Pigment Yellow 93, C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I.Pigment Yellow 139, C.I. Pigment Yellow 154, C. I. Pigment Yellow 185,C.I. Pigment Yellow 180, C.I. Pigment Red 122, C.I. Pigment Red 184, andbridged aluminum phtalocyanine pigments.

Furtheron the pigment may be chosen from those disclosed in IndustrialOrganic Pigments, Production, Properties, Applications, second edition,W. Herbst, K. Hunger; VCH, 1997.

Most preferred pigments are Pigment Yellow 128, 93, 17, 74, 138, 139,154, 185, 180; Pigment Red 122, 57:1, 184; Pigment Blue 15:3, 15:4, andcarbon black.

The pigment may, but need not, be in the form of a dispersion comprisinga dispersant also called pigment stabilizer. The latter may be, forexample, of the polyester, polyurethane of polyacrylate type, especiallyin the form of high molecular weight block copolymer, and wouldtypically be incorporated at 2.5% to 100% by weight of the pigment.Suitable examples are DISPERBYK (ex BYK Chemie) or SOLSPERSE (ex Zeneca)dispersants. A detailed list of non-polymeric as well as some polymericdispersants appears in, for example, McCutcheon's Functional Materials,North American Edition, Manufacturing Confectioner Publishing Co., GlenRock, N.J., pp. 110-129 (1990), the entire disclosure of which isincorporated herein by reference.

Other pigment stabilizers are disclosed in DE 19636382, U.S. Pat. No.5,720,802, U.S. Pat. No. 5,713,993, PCT/GB95/02501, U.S. Pat. No.5,085,689 and GB 2303376.

The pigment or dye may be present in the ink composition in anyeffective amount, generally from about 0.5 to about 20 percent by weightof the ink.

Other Monomers, Oligomers or Reactive Diluents usable in Combinationwith the Invention Monomers

A wide variety of photopolymerisable and photocrosslinkable compoundscan be used in combination with the monomers of the present invention.

Suitable monomers include e.g. the monomers disclosed in DE-OS Nos.4005231, 3516256, 3516257, 3632657 and U.S. Pat. No. 4,629,676, and WO97/31071.

The photopolymerizable composition may also comprise polymers,prepolymers and/or oligomers and/or reactive diluents comprising one ormore polymerizable functions.

Suitable prepolymers and reactive diluents for use in radiation curablecompositions such as the ink composition of the present invention may beselected from the group consisting of unsaturatedurethane(meth)acrylates, epoxy (meth)acrylates, polyolacrylates,polyether(meth)acrylates and polyester(meth)acrylates as described e.g.in “Chemistry & Technology of UV and EB formulation for coatings, inksand paints” Vol.2: Prepolymers and Reactive diluents for UV and EBcurable formulations.” Ed. G. WEBSTER-SITA Technology—London (1996).

A survey of UV-curable coating compositions is given e.g. in theperiodical “Coating” 9/88, p. 348-353.

Other usable prepolymers and oligomers belong to the class of aliphaticand aromatic polyester-urethane acrylates. The structure ofpolyester-urethane acrylates is given in the booklet “Radiation CuredCoatings” by John R. Constanza, A. P. Silveri and Joseph A. Vona,published by Federation of Societies for Coatings Technology, 1315Walnut St. Philadelphia, Pa. 19107 USA (June 1986) p. 9.

It will be clear that all these cited monomers, prepolymers, polymersand oligomers can be used in admixture.

A preferred second oligomer used in combination with a monomer of thepresent invention is an amino modified polyether acrylate known as CN501 from Cray Valley Colo.

In a particular embodiment the second monomer, oligomer or prepolymernot belonging to the invention is the principal compound involved in theradiation curing, and the monomer according to the invention functionsas so-called “reactive diluent” in order to reduce the viscosity of thefinal ink formulation.

Other Additives

Inks of the present invention may include additives such as biocides,buffering agents, anti-mold agents, pH adjustment agents, electricconductivity adjustment agents, chelating agents, anti-rusting agents,polymerisation inhibitors, light stabilizers, and the like. Suchadditives may be included in the ink jet inks of the present inventionin any effective amount, as desired.

Examples of pH controlling agents suitable for inks of the presentinvention include, but are not limited to, acids; bases, includinghydroxides of alkali metals such as lithium hydroxide, sodium hydroxideand potassium hydroxide. The amount included will depend, of course, onthe specific component being included.

Furtheron, the ink composition of the present invention may alsocomprise surfactants and photoinitiator stabilizers. Suitablephotoinitiator stabilizers include those disclosed in EP 0 465 039.Suitable surfactants are preferably of the non-ionic type, for exampleFLUORAD FC430 (ex 3M Corp.). Such surfactants when present arepreferably included in an amount of 0.1% to 10% by weight of the totalcomposition.

Compositions according to the present invention may contain organicsolvents, such as alcohols, fluorinated solvents and dipolar aproticsolvents. Preferably methanol, ethanol, propanol, 1-butanol, 1-pentanol,2-butanol, t-butanol, glycol, glycolethers, N-methylpyrrolidone,N,N-dimethylacetamid, N, N-dimethylformamid, 2,4-pentanedione andhexafluoroaceton are used.

The ink compositions of the present invention may further comprise adendrimer.

Dendrimers are radially symmetrical molecules of a STARBURST.TM.topology comprised of an initiator core, such as nitrogen,ethyleneimine, and the like, interior layers attached to the core andcomprised of a suitable number of arms, for instance, two to four arms,each arm being comprised of repeating units with the number of repeatingunits in each arm being considered the generation of the dendrimer, andterminal groups functionality, such as, for example, a primary amineattached to the outmost generation, which dendrimers are illustrated,for example, in U.S. Pat. Nos. 4,507,466; 4,631,337, 4,558,120,4,568,737, and 4,587,329, and in Tomalia et al., Angewandte Chemie, Int.Ed. Engl. 29, 138 (1990). The size and shape of the STARBURST.TM.dendrimer molecule and the functional groups present in the dendrimermolecule can be controlled by the choice of the initiator core, thenumber of generations, and the choice of repeating units employed ateach generation.

The choice of the dendrimer components can affect the properties of thedendrimers. The initiator core type can affect the dendrimer shapeproducing, for example, spheroid-shaped dendrimers, cylindrical- orrod-shaped dendrimers, or ellipsoid-shaped dendrimers. Sequentialbuilding of generations determines the dimensions of the dendrimers andthe nature of its interior. Examples of suitable core materials includeammonia, polyfunctional alcohols, such as pentaerythritol ortris-(hydroxymethyl) ethane, 1,1,1-tris-(4′-hydroxyphenyl)ethane,polyfunctional amines, such as ethylene diamine, linearpolyethyleneimines, and the like. The chemical functionality of therepeating unit in the interior layers can include, for example,amidoamines, such as aminoethyl acetamide, imines, such as diethylenediimine, or ethers like those obtained from materials such as, forexample, 3,5-dihydroxyethyl benzyl alcohol. The terminal functionalitiesinclude, for example, amino groups, hydroxyl groups, carboxylic acidgroups, carboxylates, esters, amides, phosphates, sulfonates, and thelike. The synthesis of dendrimers usually occurs by a divergent approachthat involves the initial reaction of a monomer with the initiator core,followed by exhaustive reaction of the resulting functional groups witha difunctional compound, such as a diamine, including, for example,ethylene diamine, to afford the next generation of reactive aminogroups. Thus, for example, ethylene diamine can be suitably reactedfirst with methyl acrylate to produce a compound such as N,N,N′,N′-tetra(methyoxycarbonylethyl)ethylene diamine. The aforesaid compound can bereacted in the next step with ethylene diamine to produce an amidoaminedendrimer having a generation number of zero, a molecular weight of 517,and four primary amino groups at the surface. Repetition of the abovetwo-step procedure leads to subsequent generations.

An alternate synthetic route uses a convergent growth synthesis asdescribed in detail in Hawker et al., J. Amer. Chem. Soc., 112, 7368(1990).

The dendrimer may have other groups or segments, in addition to aminogroups. For instance, the dendrimer may have a dye covalently attachedto it, or it may have certain functional groups grafted onto it.

The dendrimers may be grated with, for example, alkylene oxide oligomersor polymers, wherein the alkylene has 1-12 carbon atoms and the degreeof polymerization of the alkylene oxide is in the range of from about 2to about 100. The amount of grafting can be in any suitable range,preferably below 50% of the amino groups, and even more preferably below10% of the amino groups. Grafting of ethylene oxide on the dendrimer canbe performed by any suitable means known to those of ordinary skill inthe art. For instance, a polyethylene glycol monomethyl ether ofsuitable molecular weight can be converted to polyethylene glycolmonomethyl ether p-toluene sulfonate by suitably reacting withp-toluenesulfonyl chloride and pyridine, and the sulfonate then reactedwith the dendrimer under suitable conditions, as known to those ofordinary skill in the art. Grafted dendrimers can also be obtained fromDendritech, Inc. in Midland, Mich.

Preferred dendrimers for use in the preparation of the ink compositionof the present invention include those having terminal aminefunctionality at the surface. It is further preferred that the dendrimerhas a molecular weight in the range from about 300 to about 100,000, ageneration number of from 0 to 10, a surface amine group concentrationof from about 3 to about 4,100, and a molecular diameter of from about 1nm to about 1000 nm. More preferred dendrimers are those having terminalprimary amine functionality. It is also more preferred that thedendrimer has a molecular weight in the range from about 500 to about30,000, a generation number of from 0 to about 5, a surface groupconcentration of from about 4 to about 150, and a molecular diameter offrom about 1 nm to about 150 nm. It is also preferred that thepolydispersity index (Mw/Mn) of the dendrimer is low, preferably in therange of from about 1.1000 to about 1.0001, and more preferably in therange of from about 1.001 to about 1.0001. Examples of dendrimersprepared by the divergent approach include the STARBURST.TM. dendrimersavailable from Dendritech, Inc. These dendrimers from Dendritech, Inc.are polyamidoamines (PAMAMs) having primary amine terminal surfacefunctionality, and made of ethylene diamine core and sequencedcopolymers of ethylene diamine and methyl acrylate. They have apolydispersity index of 1.0007.

The dendrimer is present in the ink composition in an amount sufficientto provide sufficient adhesion of the ink components to the printingsurface, and also to provide sufficient water resistance and cold andhot humidity resistance. The amount of the dendrimer is preferably inthe range of from about 0.1% to about 10% by weight, more preferably inthe range of from about 0.5% to about 2% by weight, and even morepreferably in the range of from about 1% by weight to about 2% by weightof the ink composition.

In formulating the final ink jet ink compositions of the presentinvention, certain physical properties should be satisfied. For example,ink compositions for use in ink jet recording processes should haveappropriate viscosity and surface tension characteristics. In thepresent invention, it is preferred that the ink jet ink composition hasa viscosity of from about 1 to about 50 mPa.s at 25° C. The surfacetension is preferably from 20 to 72 mN/m and most preferably from 20 to60 mN/m.

Apparatuses for radiation curing are known to those skilled in the artand are commercially available. For example, the curing proceeds withmedium pressure mercury vapour lamps with or without electrodes, orpulsed xenon lamps. These ultraviolet sources usually are equipped witha cooling installation, an installation to remove the produced ozone andoptionally a nitrogen inflow to exclude air from the surface of theproduct to be cured during radiation processing. An intensity of 40 to240 W/cm in the 200-400 nm region is usually employed. An example of acommercially available ultraviolet medium-pressure electrodeless mercuryvapour lamp is the model. VPS/I600 curing system of Fusion UV systemsLtd., UK. A pulsed xenon flash lamp is commercially available from ISTStrahlentechnik GmbH. Nürtingen, Germany. Using the Fusion model one hasalso the possibility to use metal halide doped Hg vapour or XeCl excimerlamps, each with its specific UV emission spectrum. This permits ahigher degree of freedom in formulating the curing composition: a moreefficient curing is possible using the lamp with the most appropriatespectral characteristics.

High energy ionizing radiation such as X-rays, gamma rays, beta rays andaccelerated electrons can also be used to accomplish curing of the inkcomposition.

The ink jet receiver materials to which the ink composition of thepresent invention can be jetted are not limited and include e.g. paper,coated paper, polyolefin coated paper, cardboard, wood, compositeboards, plastic, coated plastic, canvas, textile, metal and ceramics.

The present invention will now be illustrated by the following exampleswithout however being limited thereto.

EXAMPLES Preparative Example

Synthesis of 4-(vinyloxy)butylmethacrylate (compound I-2).

A solution of 200 ml methacryloylchloride in 500 ml of dry ethyl acetatewas added dropwise over 120 minutes at −10° C. to a solution of 2020 gof 1,4-butanediolmonovinylether and 160 ml of pyridine in 4000 ml of dryethyl acetate. The suspension was stirred for 1 hour at 0° C. Afterfiltration the solution was washed at 0° C. with water, and then with a2% solution of sodium bicarbonate in water and brine. The organic phasewas dried over magnesium sulphate, filtered and concentrated byevaporation. 325 g of crude compound was further purified by filtrationover silicagel (4500 g) with dichloromethane. The filtrate wasconcentrated under reduced pressure. 253 g of pure compound I-2 wasobtained (yield: 68%).

Ink Composition Examples and Ink Jet Experiments

Example 1

Free radical polymerization of non-colored inks

The general composition of the non-colored radiation curable inks of theinvention is:

-   Ultra-violet polymerizing oligomer CN 501 (amine modified polyether    acrylate, Cray Valley);-   Monomer of the invention (see table 2); the numbering of the    monomers corresponds to table 1 in the Detailed Description section,    see above;-   2-isopropylthioxanthone (Quantacure ITX, Rahn AG) as photoinitiator;-   N-methyl diethanolamine (NMDA) as co-initiator or synergist;    ethanol.

Substituting the monomer of the invention by the difunctional monomerdipropylene glycol diacrylate (Radcure DPGDA, UCB) as comparativediluent gave rise to a comparative ink composition.

All inks were prepared on a basis of a total final weight of 20 g. Allink compositions are indicated in table 2 in weight percentage:

all inks contained 2% 5% wt of NMDA, 2% wt of ethanol and 10% wt ofQuantacure ITX. Finally, the Radcure DPGDA or monomer of the inventionwas added to the CN501. The resulting mixture was stirred for a coupleof minutes until the added diluent was completely dissolved. As a thirdrespectively a fourth ink component the liquid NMDA respectively theethanol was added while stirring for about five minutes to complete thesolution step. As the last compound the solid photoinitiator QuantacureITX was added. The resulting mixture was stirred for about 1 hour inorder to completely dissolve the ITX.

TABLE 2 ink composition of non-colored inks of the invention for freeradical polymerization Monomer of the invention wt % Ink (chem. wt wt %wt % Quantacure number nature) wt % % CN501 NMDA ethanol ITX 1-0**(compar 33.2 49.8 5.0 2.0 10.0 ative): DPGDA 1-1 1.1 33.2 49.8 5.0 2.010.0 1-2 1.1 41.5 41.5 5.0 2.0 10.0 1-3 1.2 33.2 49.8 5.0 2.0 10.0 1-41.2 41.5 41.5 5.0 2.0 10.0 1-5 1.4 33.2 49.8 5.0 2.0 10.0 1-6 1.4 41.541.5 5.0 2.0 10.0 1-7 1.5 33.2 49.8 5.0 2.0 10.0 1-8 1.5 41.5 41.5 5.02.0 10.0

After measuring viscosities, each ink composition was coated repeatedlyon a clear unsubbed 100 μm thick polyester film, using a bar coater anda 10 μm wired bar. The coated films were placed on a conveyer belt andtransported underneath a UV lamp. A Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/I600 lamp (H bulb), powered at 60% and 100% of thenominal maximum input power, was used to cure the coated inks. Differenttransportation speeds are used for the same coated ink composition inorder to determine the maximum speed at which curing was possible. Thelowest belt speed that could be used with the conveyer was 9 m/min, thehighest was 70 m/min. By means of a scratch test with a cotton bud, thecuring was visually evaluated: when the coating did not remain visuallyunchanged after scratching, the curing was not complete. The highestcuring speed was the highest transportation speed at which the coatingremained unchanged after scratching. This maximum speed is indicated intable 3, together with the viscosities of the corresponding ink.

TABLE 3 free radical polymerization of ink compositions with themonomers of the invention Maximum curing speed (m/min) when Power is:Viscosity 100% Ink number (mPasec) 60% of maximum P (= maximum P) 1-0**(compara.) 24 50 70 1-1 10 9 12 1-2 7 5 12 1-3 12 9 15 1-4 10 9 15 1-513 12 20 1-6 8 9 15 1-7 12 12 20 1-8 11 9 12

As one can see from table 3, all inks wherein the comparative DPGDA wasreplaced by a monomer of the invention showed a much lower viscosity ofthe radiation curable ink, and curing of these inks was still possibleusing conventional UV curing systems. The lower viscosity is of utmostimportance if one wants to use these inks in ink jet printheads.

Example 2

Free Radical Polymerization of Black Inks

The general composition of the black colored radiation curable inks ofthe invention was:

-   Ultraviolet polymerizing oligomer CN 501 (amine modified polyether    acrylate, Cray Valley)-   Monomer of the invention (see table 4),-   N-methyl diethanol amine (NMDA as co-initiator or synergist Ethanol-   2-isopropylthioxanthone (Quantacure ITX, Rahn AG)-   Special black 250 (Degussa)-   Solpserse 24000SC (Zeneca)

Substituting the monomer of the invention by the difunctional monomerdipropylene glycol diacrylate (Radcure DPGDA, UCB) as comparativediluent gave rise to a comparative ink composition. All inks wereprepared on a basis of a total final weight of 20 g. All inkcompositions are indicated in table 3 in weight percentage: they allcontained 2% 5% wt of NMDA, 2% wt of ethanol and 10% wt of QuantacureITX.

Firstly, the Radcure DPGDA or monomer of the invention was added to theCN501. The resulting mixture was stirred for a couple of minutes untilthe added diluent was completely dissolved. As a third ink component—10wt % admixture of Solsperse 24000SC in CN501 —was added while stirringfor about five minutes to complete the solution step. After furtheradding the Special Black, the resulting ink was milled for 24 hour in aball mill. Furtheron the NMDA and the ethanol were added, and theresulting mixture was stirred for about 5 minutes. As the last compoundthe solid photoinitiator Quantacure ITX was added. The resulting mixturewas stirred for about 1 hour in order to completely dissolve the ITX.The ink compositions that have been tested are given in table 4.

TABLE 4 ink composition of black colored inks of the invention for freeradical polymerization Monomer of the wt % invention wt % Special wt %Ink (chem. wt wt % wt % solsperse Black Quantacure number nature) wt % %CN501 NMDA ethanol 24000CS 250 ITX 2-0 **(compar 28.2 49.05 5.0 2.0 0.755.0 10.0 ative): DPGDA 2-1 1.1 28.2 49.05 5.0 2.0 0.75 5.0 10.0 2-2 1.228.2 49.05 5.0 2.0 0.75 5.0 10.0 2-3 1.4 28.2 49.05 5.0 2.0 0.75 5.010.0 2-4 1.5 28.2 49.05 5.0 2.0 0.75 5.0 10.0

After the viscosities had been measured, each ink composition wastreated similarly as the inks described in example 1: barcoating, curingat different belt speed and determining the maximum curing speed.Results of the experiments are given in table 5.

TABLE 5 free radical polymerization of black ink compositions with themonomers of the invention Maximum curing Viscosity speed (m/min) at Inknumber (mPasec) 100% power 2-0 **(compar.) 58 40 2-1 28 20 2-2 32 20 2-332 20 2-4 35 20

As can be seen from table 5, all black inks wherein the comparativeDPGDA was replaced by a monomer of the invention showed up a much lowerviscosity of the radiation curable ink, and curing of these inks wasstill possible using conventional UV curing systems. The lower viscosityis of utmost importance if one wants to use these inks in ink jetprintheads.

Example 3

Cationic Polymerization of Non-Colored Inks

The general composition of the non-colored radiation curable inks of theinvention was:

-   Ultra-violet: polymerizing base epoxidle resin UTVR6105 (3,4    epoxycyclohexylmethyl 3, 4 epoxycyclohexane carboxylate; Union    Carbide Corporation);-   Monomer of the invention (see table 6);-   ethanol;-   UV 9380 C: according to the MSDS of GE Silicones: a mixture of 1-5    wt % of 2-isopropylthioxanthone, 30-60 wt % C12 & C14    alkylglycidylethers, 30-60 wt % bis (4-dodecylphenyl)    iodoniumhexafluoroantimonate, 5-10 wt % linear alkylate    dodecylbenzene.

Substituting the monomer of the invention by the monofunctional epoxideUV 6216 (1,2 epoxyhexadecane) as comparative diluent gave rise to acomparative ink composition.

All inks were prepared on a basis of a total final weight of 20 g. Allink compositions are indicated in table 6 in weight percentage: they allhad 2% wt of ethanol and 10% wt of UV 9380C. Firstly, the UVR6216 ormonomer of the invention was added to the W VR6105. The resultingmixture was stirred for a couple of minutes until the added diluent wascompletely dissolved. As a second ink component the ethanol was addedwhile stirring for about five minutes to complete the solution step. Asthe last compound the photoinitiator UV9380C was added. The resultingmixture was stirred for about 1 hour in order to completely dissolve thephotoinitiator.

TABLE 6 ink composition of non-colored inks of the invention forcationic polymerization Ink Monomer of the invention wt % wt % wt % UVnumber chem. nature wt % UVR6105 ethanol 9380C 2-0 **comp. UVR6216 35.252.8 2.0 10.0 2-1 1.1 35.2 52.8 2.0 10.0 2-2 1.2 35.2 52.8 2.0 10.0 2-31.4 35.2 52.8 2.0 10.0 2-4 1.4 44.0 44.0 2.0 10.0 2-5 1.5 35.2 52.8 2.010.0 2-6 1.5 44.0 44.0 2.0 10.0

After the viscosities were measured each ink composition was treatedsimilarly as the inks described in example 1: barcoating, curing atdifferent belt speed and determining the maximum curing speed. Resultsof the experiments are given in table 7.

TABLE 7 cationic polymerization of ink compositions with the monomers ofthe invention Maximum curing speed (m/min) when Power is: Viscosity 100%Ink number (mPasec) 60% of maximum P (= maximum P) 2-0 **(compara.) 2270 70 2-1 12 30 70 2-2 13 50 70 2-3 16 30 70 2-4 12 30 70 2-5 17 50 702-6 13 30 70

As one can see from table 7, all inks wherein the comparative UVR6216was replaced by a monomer of the invention showed a much lower viscosityof the radiation curable ink, and excellent curing of these inks wasstill possible using conventional UV curing systems. The lower viscosityis of utmost importance if one wants to use these inks in ink jetprintheads.

Example 4

Cationic Polymerization of Black Colored Inks

The general composition of the black colored radiation curable inks ofthe invention was:

-   Ultraviolet polymerizing base epoxide resin UVR6105(3,4    epoxycyclohexylmethyl 3,4 epoxycyclohexane carboxylate; Union    Carbide Corporation)-   Monomer of the invention (see table 8)-   Ethanol-   UV 9380 C: according to the MSDS of GE Silicones: a mixture of 1-5    wt % of ²-isopropylthioxanthone, 30-60 wt % C12 & C14    alkylglycidylethers, 30-60 wt % bis (4-dodecylphenyl)    iodoniumhexafluoroantimonate, 5-10 wt % linear alkylate    dodecylbenzene-   Special black 250 (Degussa)-   Admixture of 10 wt % Solpserse 24000SC (Zeneca) in UVR6216

Substituting the monomer of the invention by the monofunctional epoxideUVR 6216 (1,2 epoxyhexadecane) as comparative diluent gave rise to acomparative ink composition.

All inks were prepared on a basis of a total final weight of 20 g. Allink compositions are indicated in table 8 in weight percentage: they allcontained 2% wt of ethanol and 10% wt of UV 9380C.

Firstly, the UVR6216 or monomer of the invention was added to theUVR6105. The resulting mixture was stirred for a couple of minutes untilthe added diluent was completely dissolved. As a third ink component, anadmixture of 10 wt % SOLSPERSE 24000SC in UVR 6216, was added whilestirring for about five minutes. After further adding the Special Black,the resulting ink was milled for 24 hour in a ball mill. As the lastcompound the photoinitiator UV9380C was added. The resulting mixture wasstirred for about 1 hour in order to completely dissolve thephotoinitiator.

TABLE 8 ink composition of black colored inks of the invention forcationic polymerization Monomer of the wt % invention wt % Special wt %Ink (chemical) wt % Solsperse Black wt % UV number nature wt % UVR610524000SC 250 ethanol 9380C 4-0 **(comparative) 30.2 45.3 0.75 5.0 2.010.0 UVR6216 4-1 1.1 30.2 45.3 0.75 5.0 2.0 10.0 4-2 1.2 30.2 45.3 0.755.0 2.0 10.0 4-3 1.4 30.2 45.3 0.75 5.0 2.0 10.0 4-5 1.5 30.2 45.3 0.755.0 2.0 10.0

Again, as in example 2 for the black colored inks for free radicalpolymerization, the viscosities were measured, and each ink compositionwas treated similarly as the inks already described in the foregoingexamples. Results of the experiments are given in table 9.

TABLE 9 Cationic free radical polymerization of black ink compositionswith the monomers of the invention Viscosity Maximum curing speed Inknumber (mPasec) (m/min) at 100% power 4-0 **(compar.) 24 40 4-1 18 404-2 21 40 4-3 23 30 4-4 22 30

Although the differences in viscosity are not as big as in the clearinks—mainly as a result of the addition of a black colored pigment,leading to an overall higher viscosity—it can be seen from table 9 thatintroduction of the monomers of the present invention resulted in alower viscosity. Curing of the inks was still possible usingconventional UV curing systems.

1. An ultraviolet curable ink composition for ink jet printing comprising an ultraviolet curable monomer represented by the following general formula I:

wherein, R¹ represents hydrogen, or a substituted or unsubstituted alkyl group, L represents a linking group, wherein the linking group is an aliphatic chain of at least three carbon atoms, X represents O, S or NR² wherein R² has the same meaning as R¹; when X=NR², L and R² may form together a ring system, m and n independently represent a value from 1 to
 5. 2. Ultraviolet curable ink composition for ink jet printing according to claim 1 wherein said composition further contains a colorant.
 3. Ultraviolet curable ink composition for ink jet printing according to claim 2 wherein said colorant is a dispersed pigment.
 4. Ultraviolet curable ink composition for ink jet printing according to claim 3 wherein said pigment is chosen from the list consisting of Pigment Yellow 128, 93, 17, 74, 138, 139, 154, 180, 185; Pigment Red 122, 57:1, 184; Pigment Blue 15:3, Pigment Blue 15:4 and carbon black.
 5. Ultraviolet curable ink composition for ink jet printing according to claim 1 wherein said composition further contains a photoinitiator or a mixture of photoinitiators.
 6. Ultraviolet curable ink composition for ink jet printing according to claim 5 wherein said composition further contains an initiator synergist.
 7. Ultraviolet curable ink composition for ink jet printing according to claim 1 wherein said ink composition further contains a second photopolymerizable monomer, oligomer or prepolymer and the monomer represented by formula (I) serves as reactive diluent.
 8. Ultraviolet curable ink composition for ink jet printing according to claim 7 wherein said second monomer is selected from the group consisting of the following chemical classes: an amino modified polyether acrylate, a cycloaliphatic epoxy compound, an urethane acrylate, a polyester acrylate, a polyether acrylate, and an epoxy acrylate.
 9. Ultraviolet curable ink composition for ink jet printing according to claim 1 wherein the viscosity of said ink composition is comprised between 1 and 75 mPa.s at 25° C.
 10. Ultraviolet curable ink composition for ink jet printing according to claim 1 further comprising a dendrimer.
 11. Process for obtaining a monochrome or multicolor ink jet image comprising jetting one or more streams of ink droplets having a composition according to any one of the previous claims to a receiver element, and subjecting the obtained image to ultraviolet curing.
 12. Process according to claim 11 wherein said ultraviolet curing is performed by means of one or more ultra-violet sources.
 13. An ultraviolet curable ink composition for ink jet printing comprising a free radical photoinitiator, an amine co-initiator and a radiation curable monomer represented by formula I:

wherein, R ¹ represents hydrogen, or a substituted or unsubstituted alkyl group, L represents a linking group, X represents O, S or NR ² wherein R ² has the same meaning as R ¹ ; when X=NR ² , L and R ² may form together a ring system, m and n independently represent a value from 1 to 5, characterized in that said radiation-curable monomer represented by said formula I is selected from the group consisting of:

 and wherein the viscosity of said ink composition is between 1 and 75 mPa.s at 25° C.
 14. Ultraviolet curable ink composition according to claim 13, wherein said composition further contains a colorant.
 15. Ultraviolet curable ink composition according to claim 14, wherein said colorant is a dispersed pigment.
 16. Ultraviolet curable ink composition according to claim 15 wherein said pigment is chosen from the list consisting of Pigment Yellow 128, 93, 17, 74, 138, 139, 154, 180, 185; Pigment Red 122, 57:1, 184; Pigment Blue 15:3, Pigment Blue 15:4 and carbon black.
 17. Ultraviolet curable ink composition according to claim 13, wherein said composition contains a mixture of photoinitiators.
 18. Ultraviolet curable ink composition according to claim 13, wherein said ink composition further contains a second photopolymerizable monomer, oligomer or prepolymer and the monomer represented by formula (I) serves as reactive diluent.
 19. Ultraviolet curable ink composition according to claim 18, wherein said second monomer is chosen from the group consisting of following chemical classes: an amino modified polyether acrylate, a cycloaliphatic epoxy compound, an urethane acrylate, a polyester acrylate, a polyether acrylate, and an epoxy acrylate.
 20. Ultraviolet curable ink composition according to claim 13, wherein said radiation curable ink composition further comprising a dendrimer.
 21. Ultraviolet curable ink composition according to claim 13, wherein the co-initiator is aminobenzoate co-initiator.
 22. Ultraviolet curable ink composition according to claim 13 wherein the photoinitiator is copolymerizable.
 23. Process for obtaining multicolour ink jet image comprising the steps of jetting one or more streams of ink droplets having a composition according to claim 13 to a receiver element, and subjecting the obtained image to radiation curing. 